I Love My Friends

So one of my close friends is in a relationship for like 8 months now. It was all great until he told me he was feeling less happy lately. He didn't really know why, but the feeling got worse. After hours of talking, I found out that he feels like he's being suffocated in their relation. His boyfriend wants him all the time, like day and night, which causes my friend to feel like he's losing his other friends. When he tries to talk about it, his bf gets angry, coz he see it as a sign that my friend loves him less. He feels terrible about it, coz he loves his boyfriend to death, but by forbidding him to have some time of his own, of even talking to his friends, his boyfriend just pushes him away further and further.
He asked me for advice. And although I've seen this happen many times before, (telling others what to do, claiming ur boyfriend at the cost of his friends) I don't know what to say. Coz these things always end bad.
My friend knows in his mind that this can't go on, that he has to be himself instead if who his bf wants him to be, but that damn heart is in the way...
Any decent advice on what I should tell him?